The West Side Union High School District was organized in September 1921. Conferences were held the first year and a half to determine whether the District should unite with the Mountain View, Palo Alto, or Santa Clara School Districts. In May 1923, it was unanimously decided to start a high school in the District. The school started on May 2 in rooms of the Sunnyvale Grammar School building. The Board hired Miss Leslie G. Smith as principal at $125 per month, two teachers for $225 and $200 per month, and a “janitress” for $35 per month.

In June 1923, the Board purchased the present site of Fremont High School and constructed a temporary school building. Miss May Helena Morrison was hired to teach for $2,000 a year and she taught for 28 years in the District.

In October 1923, night classes were established. Basketball, volleyball and tennis courts were installed with hot oil and sand. Only pupils, children, and residents of the West Side Union High School District could use the courts with a permit from the principal.

In March 1924, the Board agreed that a new building was needed to take care of the 400 pupils. Architect W.H. Weeks said he would draw sketches and submit plans and preliminary work for no financial obligation. He proposed that if the bonds to build the school passed, then the Board would hire him for a fee of 6% of the building costs. The bond election for $250,000 on June 4th failed. In September, 50 Sunnyvale residents petitioned the Board to call another bond election. The second bond election, this time for $225,000, was held in November and it, too, failed. In January 1925, 300 residents petitioned for yet another bond election set for $250,000. On February 24, 1925 this third bond election passed with “659 yes” and “293 no” votes. W.H. Weeks was hired as the architect at 6% and A.C. Butcher was given the charge of planting trees around the school site.

On March 27, 1925 Verne Hall was hired as the principal for the 1925-26 school year for $3,600 per year. On this date, the Board of Trustees unanimously voted to change the name of the high school to Fremont Union High School in the Fremont Union High School District. The district office was built at 589 W. Fremont Avenue in 1960-61.